Fix the nfs related daemons so that they don't intermittently

Fix the nfs related daemons so that they don't intermittently
fail with "bind: address already in use". This problem was reported
to the freebsd-stable@ mailing list on Feb. 19 under the subject
heading "statd/lockd startup failure" by george+freebsd at m5p dot com.
The problem is that the first combination of {udp,tcp X ipv4,ipv6}
would select a port# dynamically, but one of the other three combinations
would have that port# already in use. The patch is somewhat involved
because it was requested by dougb@ that the four combinations use the
same port# wherever possible. The patch splits the create_service()
function into two functions. The first goes as far as bind(2) in a
loop for up to GETPORT_MAXTRY - 1 times, attempting to use the same port#
for all four cases. If these attempts fail, the last attempt allows
the 4 cases to use different port #s. After this function has succeeded,
the second function, called complete_service(), does the rest of what
create_service() did.
The three daemons mountd, rpc.lockd and rpc.statd all have a
create_service() function that is patched in a similar way. However,
create_service() has non-trivial differences for the three daemons
that made it impractical to share the same functions between them.

Reviewed by:	jhb
MFC after:	2 weeks