MFC r317566:

Don't pass size_t arguments to setsockopt(SO_SNDBUF/SO_RCVBUF).

These commands take an int. The tests work by accident on little-endian,
64-bit systems.

PR: 218919
Tested with: qemu-cheri and CheriBSD built for mips64
Reviewed by: asomers, ngie
Obtained from: CheriBSD
Sponsored by: DARPA, AFRL