Remove unused mtag variable.

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC
Remove code related to PACKET_TAG_IPSEC_IN_CRYPTO_DONE mbuf tag.
It isn't used in FreeBSD.

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC
Remove now unused mtag argument from ipsec*_common_input_cb.

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC