network: move logging from route_set_netlink_message() to the callers

Overall size change for the whole series:
$ size build/systemd-networkd{.0,}
   text	   data	    bss	    dec	    hex	filename
1878634	 394016	     36	2272686	 22adae	build/systemd-networkd.0
1755066	 394080	     36	2149182	 20cb3e	build/systemd-networkd

i.e. 121 kb.