MAINTAINERS: Add ethtool.h to NETWORKING [GENERAL]

This is part of an effort to assign a section in MAINTAINERS to header
files related to Networking. In this case the files named ethool.h.

Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241210-mnt-ethtool-h-v1-1-2a40b567939d@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: horms

MAINTAINERS

@@ -16335,6 +16335,7 @@ F:	Documentation/networking/
 F:	Documentation/networking/net_cachelines/
 F:	Documentation/process/maintainer-netdev.rst
 F:	Documentation/userspace-api/netlink/
+F:	include/linux/ethtool.h
 F:	include/linux/framer/framer-provider.h
 F:	include/linux/framer/framer.h
 F:	include/linux/in.h
@@ -16349,6 +16350,7 @@ F:	include/linux/rtnetlink.h
 F:	include/linux/seq_file_net.h
 F:	include/linux/skbuff*
 F:	include/net/
+F:	include/uapi/linux/ethtool.h
 F:	include/uapi/linux/genetlink.h
 F:	include/uapi/linux/hsr_netlink.h
 F:	include/uapi/linux/in.h