scripts/kernel-doc: handle function pointer prototypes

scripts/kernel-doc: handle function pointer prototypes

There are some function pointer prototypes inside the net
includes, like this one:

	int (*pcs_config)(struct phylink_config *config, unsigned int mode,
			  phy_interface_t interface, const unsigned long *advertising);

There's nothing wrong using it with kernel-doc, but we need to
add a rule for it to parse such kind of prototype.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/fec520dd731a273013ae06b7653a19c7d15b9562.1592895969.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>