meson: add a couple missing networking dependencies

meson: add a couple missing networking dependencies

As evidenced in config.mak.uname and configure.ac, there are various
possible scenarios where these libraries are default-enabled in the
build, which mainly boils down to: SunOS. -lresolv is simply not the
only library that, when it exists, probably needs to be linked to for
networking.

Check for and add -lnsl -lsocket as well.

Signed-off-by: Eli Schwartz <eschwartz@gentoo.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>