resolvctl: only remove protocol after last dot when mangling ifname for resolvconf

ifname_resolvconf_mangle is supposed to remove protocol suffixes like .dhcp
from interface names. But this removed also valid parts of the ifname like
VLAN IDs, e.g. enp2s0u4.72.dhcp -> enp2s0u4 instead of enp2s0u4.72

After this change, everything behind the last dot is removed instead of the first.

src/resolve/resolvectl.c

@@ -138,7 +138,7 @@ int ifname_resolvconf_mangle(const char *s) {
 
         assert(s);
 
-        dot = strchr(s, '.');
+        dot = strrchr(s, '.');
         if (dot) {
                 _cleanup_free_ char *iface = NULL;