Add if_ipsec.ko symlink to ipsec.ko kernel module.

This add ability to automatically load ipsec kernel module, when
if_ipsec(4) virtual interface is created using ifconfig(8).

Reviewed by:	gallatin
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D20169

sys/modules/ipsec/Makefile

@@ -7,6 +7,7 @@ SRCS=	if_ipsec.c ipsec.c ipsec_input.c ipsec_mbuf.c ipsec_mod.c \
 	ipsec_output.c xform_ah.c xform_esp.c xform_ipcomp.c \
 	opt_inet.h opt_inet6.h opt_ipsec.h opt_sctp.h 
 SRCS.INET=	udpencap.c
+SYMLINKS=	${KMOD}.ko ${KMODDIR}/if_${KMOD}.ko
 
 opt_ipsec.h:
 	@echo "#define IPSEC_SUPPORT 1" > ${.TARGET}