MAINTAINERS: Add "B:" field for networking.

We want people to report bugs to the netdev list.
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -8761,6 +8761,7 @@ W:	http://www.linuxfoundation.org/en/Net
 Q:	http://patchwork.ozlabs.org/project/netdev/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git
+B:	mailto:netdev@vger.kernel.org
 S:	Maintained
 F:	net/
 F:	include/net/