gsocket: Fix build error on Android
imr_interface.s_addr is not defined in the HAVE_IP_MREQN case. https://bugzilla.gnome.org/show_bug.cgi?id=740791
imr_interface.s_addr is not defined in the HAVE_IP_MREQN case. https://bugzilla.gnome.org/show_bug.cgi?id=740791
mentioned in commit 51e53244