LinuxKPI: 802.11: zero-pad debug flags

Write the debug flags as full 32bit hex numbers to have a better
view on them.

No functional changes.

Sponsored by: The FreeBSD Foundation
Reviewed by: cc, emaste
Differential Revision: https://reviews.freebsd.org/D42426

(cherry picked from commit 8895b47638ea4d7a13fba97afe8cd9faacfdda83)