netfilter: nf_ct_h323: Extend nf_h323_error_boundary to work on bits as well

This patch fixes several out of bounds memory reads by extending
the nf_h323_error_boundary() function to work on bits as well
an check the affected parts.

Signed-off-by: Eric Sesterhenn <eric.sesterhenn@x41-dsec.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>