libs/libc/netdb: Fix a link error in lib_gethostbynamer.c with protected build. NOTE: g_lo_ipv4addr also exists in net/loopback/lo_globals.c which can be linked with kernel build only. Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com> Approved-by: GregoryN <gnutt@nuttx.org>