sm-notify: "-v hostname" doesn't work when IPV6_SUPPORT is enabled

sm-notify: "-v hostname" doesn't work when IPV6_SUPPORT is enabled

Marc Eshel reports that using the -v command line option on the
sm-notify command stopped working after nfs-utils 1.2.2, when IPv6
support was added.  If nfs-utils is built without IPv6 support, it
still works.  Marc specified a hostname with a single A record.

smn_bind_address() must construct a bind address with the same
family as the RPC socket's protocol family.  Add an AI_V4MAPPED hint
so an appropriate IPv6 bind address is constructed even if -v
specifies an IPv4 presentation address, or a hostname with only IPv4
mappings.

We still use an IPv4 bind address if IPv6 support is compiled out or
the host does not support IPv6.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>
Cc: Marc Eshel <eshel@us.ibm.com>