MAINTAINERS: Add connector headers to NETWORKING DRIVERS

Commit 46cf789b

 ("connector: Move maintainence under networking
drivers umbrella.") moved the connector maintenance but did not include
the connector header files.

It seems that it has always been implied that these headers were
maintained along with the rest of the connector code, both before and
after the cited commit. Make this explicit.

Signed-off-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>