[PATCH] knfsd: SUNRPC: add a "generic" function to see if the peer uses a secure port

The only reason svcsock.c looks at a sockaddr's port is to check whether the
remote peer is connecting from a privileged port.  Refactor this check to hide
processing that is specific to address format.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: Aurelien Charbon <aurelien.charbon@ext.bull.net>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>