pcapng: convert FCS lengths between bytes and bits.

The FCS length in a pcapng IDB is in bits, but the length in an EPB is in bytes; convert the latter to bits.

The FCS length in the Ethernet pseudo-header is in bytes; convert the length-in-bits to a length-in-bytes before using it to set the FCS length in the pseudo-header.

Fixes #19174 (closed).

(backported from commit a3fd4fd2)

approved this merge request

assigned to @ws-gitlab-utility

merged