pgsql: In contrib/uuid-ossp, #include headers needed for ntohl() and nt

In contrib/uuid-ossp, #include headers needed for ntohl() and ntohs().

Oversight in commit b8cc8f947. I just noticed this causes compiler
warnings on FreeBSD, and it really ought to cause warnings elsewhere too:
all references I can find say that <arpa/inet.h> is required for these.
We have a lot of code elsewhere that thinks that both <netinet/in.h>
and <arpa/inet.h> should be included for these functions, so do it that
way here too, even though <arpa/inet.h> ought to be sufficient according
to the references I consulted.

Back-patch to 9.4 where the previous commit landed.

Branch
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REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/20c27fdfd3af8da68837ab1cbea08100619f91b6

Modified Files
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contrib/uuid-ossp/uuid-ossp.c | 4 ++++
1 file changed, 4 insertions(+)