mptcp: include inet_common in mib.h

So this file is now self-contained: it can be compiled alone with
analytic tools.
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20240514011335.176158-9-martineau@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/mib.h

 /* SPDX-License-Identifier: GPL-2.0-or-later */
 
+#include <net/inet_common.h>
+
 enum linux_mptcp_mib_field {
 	MPTCP_MIB_NUM = 0,
 	MPTCP_MIB_MPCAPABLEPASSIVE,	/* Received SYN with MP_CAPABLE */