ipfilter: Fix use after free on packet with broken lengths

Under the scenario with a packet with length of 67 bytes, a header length
using the default of 20 bytes and a TCP data offset (th_off) of 48 will
cause m_pullup() to fail to make sure bytes are arragned contiguously.
m_pullup() will free the mbuf chain and return a null. ipfilter stores
the resultant mbuf address (or the resulting NULL) in its fr_info_t
structure. Unfortuntely the eroneous packet is not flagged for drop.
This results in a kernel page fault at line 410 of sys/netinet/ip_fastfwd.c
as it tries to use a now previously freed, by m_pullup(), mbuf.

PR: 266442
Reported by: Robert Morris <rtm@lcs.mit.edu>
MFC after: 1 week