This saves approx 50 bytes of storage for the session structure
and puts us comfortably below 256 bytes, at least i the IPv4 case.

Spotted by: c0004x.vtc on slow machines.

Suggested by:	scoof

Yay, gcc.  Or something.

There is no way to disable warn_unused_result and glibc (or the gcc
fortification patches) add that to write in higher optimisation
levels.  We'll take the warning, but not make it fatal.

See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25509 for the relevant
gcc bug report.