mgcp: Include enough socket data structures to build on freebsd

in_address is not 'accidently' included by FreeBSD when we include
the osmocom/core/select.h header file. We need to include a bit
more.

In file included from mgcp_protocol.c:38:
../../include/openbsc/mgcp_internal.h:134:21: error: field has incomplete type 'struct sockaddr_in'
        struct sockaddr_in forward;
1 file changed
tree: 63ac7fb85fdc9887b30612bbe94c97c6d0096283
  1. debian/
  2. hlrsync/
  3. linux-kernel/
  4. openbsc/
  5. wireshark/
  6. .gitignore
  7. README