Fix a panic when handling fragmented ip4 packets with 'drop-ovl' set.
In that scenario we take a different branch in pf_normalize_ip(), taking us to pf_fragcache() (rather than pf_reassemble()). In pf_fragcache() we create a pf_fragment, but do not set the address family. This leads to a panic when we try to insert that into pf_frag_tree because pf_addr_cmp(), which is used to compare the pf_fragments doesn't know what to do if the address family is not set.
Simply ensure that the address family is set correctly (always AF_INET in this path).
PR: 200330