Fix build on FreeBSD

Fix build on FreeBSD

Commit 24758c5f (Replace gettimeofday() by clock_gettime()) removed
the inclusion of sys/time.h from several files since this header was
believed to be needed only for gettimeofday(), which was removed in
the same commit.

However, this broke the build on FreeBSD since sys/time.h
also pulled in the declaration of u_short, which is required by
/usr/include/netinet/udp.h. Therefore the compilation of udp_send.c
failed with

	/usr/include/netinet/udp.h:42: error: expected specifier-qualifier-list before 'u_short'

This patch changes udp_send.c to include sys/types.h, which provides
the missing declaration.