text-based mount: Support protocol family negotiation

text-based mount: Support protocol family negotiation

Jeff Layton pointed out that the current negotiation logic in
stropts.c simply doesn't handle the case where a server may have an
IPv6 address and an IPv4 address, but only NFS/IPv4 is supported.
This is typical of all currently deployed Linux servers.

Add support for trying all addresses returned from DNS when
"proto=" is not specified on the command line.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>