Disable UDP pass of gssrpc tests on all platforms

Disable UDP pass of gssrpc tests on all platforms

The AUTH_GSSAPI flavor of rpc authentication uses IP address channel
bindings.  These are broken over UDP, because svcudp_recv() fails to
get the destination address of incoming packets (it tries to use the
recvmsg() msg_name field to get the destination IP address, which
instead gets the source address; see ticket #5540).

There is no simple or comprehensive way to fix this; using IP_PKTINFO
is a fair amount of code and only works on some platforms.  It's also
not very important--nobody should be using AUTH_GSSAPI except perhaps
for compatibility with really old kadmin, and kadmin only runs over
TCP.  Since the gssrpc tests are closely wedded to AUTH_GSSAPI, the
simplest fix is to only run the TCP pass.