log: add an "error" parameter to all low-level logging calls and intrdouce log_error_errno() as log calls that take error numbers

This change has two benefits:

- The format string %m will now resolve to the specified error (or to
  errno if the specified error is 0. This allows getting rid of a ton of
  strerror() invocations, a function that is not thread-safe.

- The specified error can be passed to the journal in the ERRNO= field.

Now of course, we just need somebody to convert all cases of this:

        log_error("Something happened: %s", strerror(-r));

into thus:

        log_error_errno(-r, "Something happened: %m");

src/libsystemd-network/dhcp-internal.h

@@ -71,4 +71,4 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(sd_dhcp_client*, sd_dhcp_client_unref);
 #define DHCP_CLIENT_DONT_DESTROY(client) \
         _cleanup_dhcp_client_unref_ _unused_ sd_dhcp_client *_dont_destroy_##client = sd_dhcp_client_ref(client)
 
-#define log_dhcp_client(client, fmt, ...) log_meta(LOG_DEBUG, __FILE__, __LINE__, __func__, "DHCP CLIENT (0x%x): " fmt, client->xid, ##__VA_ARGS__)
+#define log_dhcp_client(client, fmt, ...) log_meta(LOG_DEBUG, 0, __FILE__, __LINE__, __func__, "DHCP CLIENT (0x%x): " fmt, client->xid, ##__VA_ARGS__)

src/libsystemd-network/dhcp-server-internal.h

@@ -79,7 +79,7 @@ typedef struct DHCPRequest {
 DEFINE_TRIVIAL_CLEANUP_FUNC(sd_dhcp_server*, sd_dhcp_server_unref);
 #define _cleanup_dhcp_server_unref_ _cleanup_(sd_dhcp_server_unrefp)
 
-#define log_dhcp_server(client, fmt, ...) log_meta(LOG_DEBUG, __FILE__, __LINE__, __func__, "DHCP SERVER: " fmt, ##__VA_ARGS__)
+#define log_dhcp_server(client, fmt, ...) log_meta(LOG_DEBUG, 0, __FILE__, __LINE__, __func__, "DHCP SERVER: " fmt, ##__VA_ARGS__)
 
 int dhcp_server_handle_message(sd_dhcp_server *server, DHCPMessage *message,
                                size_t length);

src/libsystemd-network/dhcp6-internal.h

@@ -56,7 +56,7 @@ struct DHCP6IA {
 
 typedef struct DHCP6IA DHCP6IA;
 
-#define log_dhcp6_client(p, fmt, ...) log_meta(LOG_DEBUG, __FILE__, __LINE__, __func__, "DHCPv6 CLIENT: " fmt, ##__VA_ARGS__)
+#define log_dhcp6_client(p, fmt, ...) log_meta(LOG_DEBUG, 0, __FILE__, __LINE__, __func__, "DHCPv6 CLIENT: " fmt, ##__VA_ARGS__)
 
 int dhcp_network_icmp6_bind_router_solicitation(int index);
 int dhcp_network_icmp6_send_router_solicitation(int s, const struct ether_addr *ether_addr);

src/libsystemd-network/ipv4ll-internal.h

@@ -35,4 +35,4 @@ void arp_packet_probe(struct ether_arp *arp, be32_t pa, const struct ether_addr
 void arp_packet_announcement(struct ether_arp *arp, be32_t pa, const struct ether_addr *ha);
 int arp_packet_verify_headers(struct ether_arp *arp);
 
-#define log_ipv4ll(ll, fmt, ...) log_meta(LOG_DEBUG, __FILE__, __LINE__, __func__, "IPv4LL: " fmt, ##__VA_ARGS__)
+#define log_ipv4ll(ll, fmt, ...) log_meta(LOG_DEBUG, 0, __FILE__, __LINE__, __func__, "IPv4LL: " fmt, ##__VA_ARGS__)

src/libsystemd-network/sd-icmp6-nd.c

@@ -54,7 +54,7 @@ struct sd_icmp6_nd {
         void *userdata;
 };
 
-#define log_icmp6_nd(p, fmt, ...) log_meta(LOG_DEBUG, __FILE__, __LINE__, __func__, "ICMPv6 CLIENT: " fmt, ##__VA_ARGS__)
+#define log_icmp6_nd(p, fmt, ...) log_meta(LOG_DEBUG, 0, __FILE__, __LINE__, __func__, "ICMPv6 CLIENT: " fmt, ##__VA_ARGS__)
 
 static void icmp6_nd_notify(sd_icmp6_nd *nd, int event)
 {