Make gcc 4 happier about x509_addr.c

Make gcc 4 happier about x509_addr.c

gcc 4 on sparc64 issues a few 'warning: value computed is not used'.
There are two cases: sk_set_cmp_function() returns the old comparison
function of the stack which we don't care about. The one warning about
an sk_delete() is about a return value that we know already and which
we will free a few lines down.

ok inoguchi miod