Verify expectations better in SockDiagTest.

Currently SockDiagTest only checks for socket errors, it does not
check that the socket was closed via SOCK_DESTROY. This can cause
us to think that SOCK_DESTROY is working when it isn't.

Fix this by checking the error codes and expecting that at least
one socket was closed by SOCK_DESTROY.

Bug: 28508161
Change-Id: Iab423dba0aa30466481dd3a7304aa8f69c5cf605