test//bio_dgram_test.c: Skip test when BIO_bind() fails

test//bio_dgram_test.c: Skip test when BIO_bind() fails

This test isn't supposed to test BIO_bind() itself, so we can be a bit
sloppy and assume that it fails because the attempted binding is not
supported on the platform where this is run.  For example, BIO_bind()
fails when it's given an IPv6 address and the platform where this is
run doesn't support that address family.

In a case like this, it's sensible enough to simply skip the test when
BIO_bind() fails.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20449)