tree-wise: several cleanups for logging

- drop unnecessary SYNTHETIC_ERRNO() when the logger does not propagate
  error code,
- drop unnecessary '%m' in error message when the error code is
  specified with SYNTHETIC_ERRNO(),
- add missing full stop at the end of log message,
- use RET_GATHER(),
- add missing ", ignoring.",
- upeercase the first letter, etc., etc...

src/network/networkctl.c

@@ -1073,9 +1073,7 @@ static int get_gateway_description(
                 }
 
                 if (type != RTM_NEWNEIGH) {
-                        log_error_errno(SYNTHETIC_ERRNO(EINVAL),
-                                        "Got unexpected netlink message type %u, ignoring",
-                                        type);
+                        log_error("Got unexpected netlink message type %u, ignoring.", type);
                         continue;
                 }
 
@@ -1086,7 +1084,7 @@ static int get_gateway_description(
                 }
 
                 if (fam != family) {
-                        log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Got invalid rtnl family %d, ignoring", fam);
+                        log_error("Got invalid rtnl family %d, ignoring.", fam);
                         continue;
                 }