Fix padding in struct tcp_info

This structure should have the same size across different FreeBSD
versions to ensure backwards-compatibility. It has since stable/6. But
two recent changes added fields without compensating by reducing
padding:
945f9a7cc9dcc071bfcc702748fbbb11087ae773 and
22c81cc51636cfebe94e0979eb31556d87775938 . Reduce padding to
compensate.

Direct commit to stable/14 because we decided to break compatibility in
FreeBSD 15 in order to add more fields. Of course, that decision could
be reversed before 15.0-RELEASE. See the review for details.

PR: 273902
MFC after: 1 week
Reviewed by: tuexen, glebius
Differential Revision: https://reviews.freebsd.org/D41894