Do not call crypto_newsession() while holding xforms_lock mutex.
Release mutex before invoking crypto_newsession(), and use
ipsec_kmod_enter()/ipsec_kmod_exit() functions to protect from doing
access to unloaded kernel module memory.
Move xform-releated functions into subr_ipsec.c to be able use
ipsec_kmod_* functions. Also unconditionally build ipsec_kmod_*
functions, since now they are always used by IPSec code.
Add xf_cntr field to struct xformsw, it is used by ipsec_kmod_*
functions. Also constify xf_name field, since it is not expected to be
modified.
Approved by: re (kib)
Differential Revision: https://reviews.freebsd.org/D17302
6c193bda23