sd-network: don't needlessly abbreviate "callback" as "cb" in struct members

It's OK to abbreviate this in the local scope, but otherwise, let's not be
needlessly terse.

src/libsystemd-network/sd-dhcp-client.c

@@ -101,7 +101,7 @@ struct sd_dhcp_client {
         sd_event_source *timeout_t1;
         sd_event_source *timeout_t2;
         sd_event_source *timeout_expire;
-        sd_dhcp_client_callback_t cb;
+        sd_dhcp_client_callback_t callback;
         void *userdata;
         sd_dhcp_lease *lease;
         usec_t start_delay;
@@ -131,9 +131,10 @@ int sd_dhcp_client_set_callback(
                 sd_dhcp_client *client,
                 sd_dhcp_client_callback_t cb,
                 void *userdata) {
+
         assert_return(client, -EINVAL);
 
-        client->cb = cb;
+        client->callback = cb;
         client->userdata = userdata;
 
         return 0;
@@ -449,8 +450,10 @@ int sd_dhcp_client_get_lease(sd_dhcp_client *client, sd_dhcp_lease **ret) {
 }
 
 static void client_notify(sd_dhcp_client *client, int event) {
-        if (client->cb)
-                client->cb(client, event, client->userdata);
+        assert(client);
+
+        if (client->callback)
+                client->callback(client, event, client->userdata);
 }
 
 static int client_initialize(sd_dhcp_client *client) {

src/libsystemd-network/sd-dhcp6-client.c

@@ -64,7 +64,7 @@ struct sd_dhcp6_client {
         uint8_t retransmit_count;
         sd_event_source *timeout_resend;
         sd_event_source *timeout_resend_expire;
-        sd_dhcp6_client_callback_t cb;
+        sd_dhcp6_client_callback_t callback;
         void *userdata;
         struct duid duid;
         size_t duid_len;
@@ -115,9 +115,10 @@ int sd_dhcp6_client_set_callback(
                 sd_dhcp6_client *client,
                 sd_dhcp6_client_callback_t cb,
                 void *userdata) {
+
         assert_return(client, -EINVAL);
 
-        client->cb = cb;
+        client->callback = cb;
         client->userdata = userdata;
 
         return 0;
@@ -292,8 +293,10 @@ int sd_dhcp6_client_get_lease(sd_dhcp6_client *client, sd_dhcp6_lease **ret) {
 }
 
 static void client_notify(sd_dhcp6_client *client, int event) {
-        if (client->cb)
-                client->cb(client, event, client->userdata);
+        assert(client);
+
+        if (client->callback)
+                client->callback(client, event, client->userdata);
 }
 
 static void client_set_lease(sd_dhcp6_client *client, sd_dhcp6_lease *lease) {

src/libsystemd-network/sd-ipv4acd.c

@@ -93,7 +93,7 @@ struct sd_ipv4acd {
         struct ether_addr mac_addr;
         sd_event *event;
         int event_priority;
-        sd_ipv4acd_callback_t cb;
+        sd_ipv4acd_callback_t callback;
         void* userdata;
 };
 
@@ -156,10 +156,10 @@ static void ipv4acd_set_state(sd_ipv4acd *ll, IPv4ACDState st, bool reset_counte
 static void ipv4acd_client_notify(sd_ipv4acd *ll, int event) {
         assert(ll);
 
-        if (!ll->cb)
+        if (!ll->callback)
                 return;
 
-        ll->cb(ll, event, ll->userdata);
+        ll->callback(ll, event, ll->userdata);
 }
 
 static void ipv4acd_stop(sd_ipv4acd *ll) {
@@ -470,7 +470,7 @@ int sd_ipv4acd_attach_event(sd_ipv4acd *ll, sd_event *event, int64_t priority) {
 int sd_ipv4acd_set_callback(sd_ipv4acd *ll, sd_ipv4acd_callback_t cb, void *userdata) {
         assert_return(ll, -EINVAL);
 
-        ll->cb = cb;
+        ll->callback = cb;
         ll->userdata = userdata;
 
         return 0;

src/libsystemd-network/sd-ipv4ll.c

@@ -52,7 +52,7 @@ struct sd_ipv4ll {
 
         /* External */
         be32_t claimed_address;
-        sd_ipv4ll_callback_t cb;
+        sd_ipv4ll_callback_t callback;
         void* userdata;
 };
 
@@ -176,7 +176,7 @@ int sd_ipv4ll_attach_event(sd_ipv4ll *ll, sd_event *event, int64_t priority) {
 int sd_ipv4ll_set_callback(sd_ipv4ll *ll, sd_ipv4ll_callback_t cb, void *userdata) {
         assert_return(ll, -EINVAL);
 
-        ll->cb = cb;
+        ll->callback = cb;
         ll->userdata = userdata;
 
         return 0;
@@ -312,8 +312,8 @@ int sd_ipv4ll_start(sd_ipv4ll *ll) {
 static void ipv4ll_client_notify(sd_ipv4ll *ll, int event) {
         assert(ll);
 
-        if (ll->cb)
-                ll->cb(ll, event, ll->userdata);
+        if (ll->callback)
+                ll->callback(ll, event, ll->userdata);
 }
 
 void ipv4ll_on_acd(sd_ipv4acd *acd, int event, void *userdata) {