Fix 342221 - socket connect produce false positive saying access to uninitialized memory area

As we check what follows af_family, the length to check must be decreased
by sizeof(af_maily)


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14835 a5019735-40e9-0310-863c-91ae7b9d1cf9