Add bounds checks and fix a length argument.

Add bounds checks and fix a length argument.

Before reading the record header of a REC_FRAME{2,4,6} record, make sure
the record length is >= the length of that header.

Whe calling fix_pseudo_header(), pass the actual length of the packet
data, not the remaining length of the record (which may include
padding), so we don't read past the end of the packet data.

Bug: 11827
Change-Id: I1c63a4cb014c4616ffdd202660e68c576f266872
Reviewed-on: https://code.wireshark.org/review/12756
Reviewed-by: Guy Harris <guy@alum.mit.edu>