rpcb_clnt.c: Do not force use of UDP

Without this patch, the code in the rpcbind client forces
the use of UDP. A comment notes that some rpcbind servers
only support UDP. This makes NFSv3 mounts to Azure servers
impossible, since they require use of TCP for rpcbind.
Since the comment is very old (imported from NetBSD in 2001)
and I do not believe any UDP only rpcbind servers will
still exist, this patch comments out the code that forces
use of UDP, so that NFSv3 mounts to Azure servers can work.

For an NFSv3 mount, the "udp" mount option will still
make mount_nfs use UDP for rpcbind so that can be used
as a workaround for any old NFSv3 server that only
supports rpcbind over UDP (if any such server still exists).

I asked if doing this change is appropriate on freebsd-fs@
and I only got one reply (off list) that supported doing
the change.

PR: 267301
MFC after: 1 month