xfrm: removes a superfluous check and add a statistic

Remove the check if x->km.state equal to XFRM_STATE_VALID in
xfrm_state_check_expire(), which will be done before call
xfrm_state_check_expire().

add a LINUX_MIB_XFRMOUTSTATEINVALID statistic to record the
outbound error due to invalid xfrm state.

Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

include/uapi/linux/snmp.h

@@ -278,6 +278,7 @@ enum
 	LINUX_MIB_XFRMOUTPOLDEAD,		/* XfrmOutPolDead */
 	LINUX_MIB_XFRMOUTPOLERROR,		/* XfrmOutPolError */
 	LINUX_MIB_XFRMFWDHDRERROR,		/* XfrmFwdHdrError*/
+	LINUX_MIB_XFRMOUTSTATEINVALID,		/* XfrmOutStateInvalid */
 	__LINUX_MIB_XFRMMAX
 };