net: add missing sk_max_pacing_rate doc

Warning(include/net/sock.h:411): No description found for parameter
'sk_max_pacing_rate'

Lets please "make htmldocs" and kbuild bot.
Reported-by: NWu Fengguang <fengguang.wu@intel.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -233,6 +233,7 @@ struct cg_proto;
   *	@sk_ll_usec: usecs to busypoll when there is no data
   *	@sk_allocation: allocation mode
   *	@sk_pacing_rate: Pacing rate (if supported by transport/packet scheduler)
+  *	@sk_max_pacing_rate: Maximum pacing rate (%SO_MAX_PACING_RATE)
   *	@sk_sndbuf: size of send buffer in bytes
   *	@sk_flags: %SO_LINGER (l_onoff), %SO_BROADCAST, %SO_KEEPALIVE,
   *		   %SO_OOBINLINE settings, %SO_TIMESTAMPING settings