Fix a use after free panic in ipfilter's fragment processing.

Memory is malloc'd, then a search for a match in the fragment table
is made and if the fragment matches, the wrong fragment table is
freed, causing a use after free panic. This commit fixes this.

A symptom of the problem is a kernel page fault in bcopy() called by
ipf_frag_lookup() at line 715 in ip_frag.c. Another symptom is a
kernel page fault in ipf_frag_delete() when called by ipf_frag_expire()
via ipf_slowtimer().

MFC after:	1 week

sys/contrib/ipfilter/netinet/ip_frag.c

@@ -474,7 +474,7 @@ ipfr_frag_new(softc, softf, fin, pass, table
 			  IPFR_CMPSZ)) {
 			RWLOCK_EXIT(lock);
 			FBUMPD(ifs_exists);
-			KFREE(fra);
+			KFREE(fran);
 			return NULL;
 		}