MAINTAINERS: Add a bugzilla link for NFSD

I recently found out about B: for noting where subsystem bugs can be
filed. I do pay attention to bugzilla.kernel.org. The Linux NFS
community has decided to steer kernel NFS issues to the kernel.org
bugzilla instead of bugzilla.linux-nfs.org.

Remove the W: entry; the sourceforge information is stale and
unmaintained.

Cc: Thorsten Leemhuis <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>

MAINTAINERS

···
 R:	Tom Talpey <[e-mail]>
 L:	[e-mail]
 S:	Supported
-W:	http://nfs.sourceforge.net/
+B:	https://bugzilla.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git
 F:	Documentation/filesystems/nfs/
 F:	fs/lockd/