doc: announce kvargs API change

doc: announce kvargs API change

After processing a kvlist in rte_kvargs_process(),
it may be needed to loop again over kvlist in order to know
whether the key is matched or not.
In order to simplify implementation of kvargs checks,
a new pointer parameter may be used to get the match count.

The change of the function prototype would be as below:

 int
 rte_kvargs_process(const struct rte_kvargs *kvlist,
 		const char *key_match,
+		int *match_count,
 		arg_handler_t handler,
 		void *opaque_arg)

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>