MAINTAINERS: Add limited globs for Networking headers

MAINTAINERS: Add limited globs for Networking headers

This aims to add limited globs to improve the coverage of header files
in the NETWORKING DRIVERS and NETWORKING [GENERAL] sections.

It is done so in a minimal way to exclude overlap with other sections.
And so as not to require "X" entries to exclude files otherwise
matched by these new globs.

While imperfect, due to it's limited nature, this does extend coverage
of header files by these sections. And aims to automatically cover
new files that seem very likely belong to these sections.

The include/linux/netdev* glob (both sections)
+ Subsumes the entries for:
  - include/linux/netdevice.h
+ Extends the sections to cover
  - include/linux/netdevice_xmit.h
  - include/linux/netdev_features.h

The include/uapi/linux/netdev* globs: (both sections)
+ Subsumes the entries for:
  - include/linux/netdevice.h
+ Extends the sections to cover
  - include/linux/netdev.h

The include/linux/skbuff* glob (NETWORKING [GENERAL] section only):
+ Subsumes the entry for:
  - include/linux/skbuff.h
+ Extends the section to cover
  - include/linux/skbuff_ref.h

A include/uapi/linux/net_* glob was not added to the NETWORKING [GENERAL]
section. Although it would subsume the entry for
include/uapi/linux/net_namespace.h, which is fine, it would also extend
coverage to:
- include/uapi/linux/net_dropmon.h, which belongs to the
   NETWORK DROP MONITOR section
- include/uapi/linux/net_tstamp.h which, as per an earlier patch in this
  series, belongs to the SOCKET TIMESTAMPING section

Signed-off-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>