network: introduce 'degraded-carrier' operstate to order all states

Previously, 'degraded' state is ambiguous for bonding or bridge master:
1. one or more slave interfaces does not have carrier,
2. no link local address is assigned to the master,
3. combination of the above two.

This makes the above case 1 and 3 are in the new 'degraded-carrier'
state, and makes 'degraded' state as all slaves are active but no
link local address on master.

src/libsystemd/sd-network/network-util.c

@@ -21,13 +21,14 @@ bool network_is_online(void) {
 }
 
 static const char* const link_operstate_table[_LINK_OPERSTATE_MAX] = {
-        [LINK_OPERSTATE_OFF] = "off",
-        [LINK_OPERSTATE_NO_CARRIER] = "no-carrier",
-        [LINK_OPERSTATE_DORMANT] = "dormant",
-        [LINK_OPERSTATE_CARRIER] = "carrier",
-        [LINK_OPERSTATE_DEGRADED] = "degraded",
-        [LINK_OPERSTATE_ENSLAVED] = "enslaved",
-        [LINK_OPERSTATE_ROUTABLE] = "routable",
+        [LINK_OPERSTATE_OFF]              = "off",
+        [LINK_OPERSTATE_NO_CARRIER]       = "no-carrier",
+        [LINK_OPERSTATE_DORMANT]          = "dormant",
+        [LINK_OPERSTATE_DEGRADED_CARRIER] = "degraded-carrier",
+        [LINK_OPERSTATE_CARRIER]          = "carrier",
+        [LINK_OPERSTATE_DEGRADED]         = "degraded",
+        [LINK_OPERSTATE_ENSLAVED]         = "enslaved",
+        [LINK_OPERSTATE_ROUTABLE]         = "routable",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(link_operstate, LinkOperationalState);

src/libsystemd/sd-network/network-util.h

@@ -11,6 +11,7 @@ typedef enum LinkOperationalState {
         LINK_OPERSTATE_OFF,
         LINK_OPERSTATE_NO_CARRIER,
         LINK_OPERSTATE_DORMANT,
+        LINK_OPERSTATE_DEGRADED_CARRIER,
         LINK_OPERSTATE_CARRIER,
         LINK_OPERSTATE_DEGRADED,
         LINK_OPERSTATE_ENSLAVED,