libcommon: eliminate socket.c

Replace calls to make_sock() with osmo_sock_init_ofd().
Shame on me for not testing every single one in practice, I hope for peer
review to confirm that this should be correct... Read closely please!

The IPPROTO_GRE define seems to be unused (at least in osmo-bsc.git), drop it
completely.

Change-Id: Ia6e4e0e1eed3328fa25b3b90be376d532ad0e56b
7 files changed