sm-notify: Don't orphan addrinfo structs

sm-notify: Don't orphan addrinfo structs

sm-notify orphans an addrinfo struct in its address list rotation
logic if only a single result was returned from getaddrinfo(3).

For each host, the first time through notify_host(), we want to
send a PMAP_GETPORT request.  ->ai is NULL, and retries is set to 100,
forcing a DNS lookup and an address rotation.  If only a single
addrinfo struct is returned, the rotation logic causes a NULL to be
planted in ->ai, copied from the ai_next field of the returned result.

This means that the second time through notify_host() (to perform the
actual SM_NOTIFY call) we do a second DNS lookup, since ->ai is NULL.
The result of the first lookup has been orphaned, and extra network
traffic is generated.

This scenario is actually fairly common.  Since we pass

  .ai_protocol = IPPROTO_UDP,

  to getaddrinfo(3), for most hosts, which have a single forward and
  reverse pointer in the DNS database, we get back a single addrinfo
  struct as a result.

  To address this problem, only perform the address list rotation if
  there is more than one element on the list returned by getaddrinfo(3).

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