pgsql: Fix network_spgist.c build failures from missing AF_INET definit

Fix network_spgist.c build failures from missing AF_INET definition.

AF_INET is apparently defined in something that's pulled in automatically
on Linux, but the buildfarm says that's not true everywhere.  Comparing
to network_gist.c suggests that including <sys/socket.h> ought to fix it,
and the POSIX standard concurs.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/32909a57f9fb131eab8971a6d9845b55bbcb9091

Modified Files
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src/backend/utils/adt/network_spgist.c | 2 ++
1 file changed, 2 insertions(+)