pkg: hook up src/boot, wow, that was easy

Makefile

@@ -214,6 +214,7 @@ scripts: want-git
 
 install: force
 	@${MAKE} -C ${.CURDIR}/contrib install DESTDIR=${DESTDIR}
+	@${MAKE} -C ${.CURDIR}/src install_boot DESTDIR=${DESTDIR}
 	@${MAKE} -C ${.CURDIR}/src install DESTDIR=${DESTDIR} \
 	    CORE_NAME=${CORE_NAME} CORE_ABI=${CORE_ABI} \
 	    CORE_PACKAGESITE=${CORE_PACKAGESITE} \

src/Makefile

 ROOT=	/usr/local
 TREES=	etc opnsense sbin wizard www
 
-EXTRA=	bootstrap
+EXTRA=	boot bootstrap
+
+ROOT_boot=	# /
+TREES_boot=	boot
 
 ROOT_bootstrap= /usr/local
 TREES_bootstrap=etc/pkg