crypto: Validate AES-GCM IV length in check_csp().

This centralizes the check for valid nonce lengths for AES-GCM.

While here, remove some duplicate checks for valid AES-GCM tag lengths
from ccp(4) and ccr(4).

Reviewed by: markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33194

(cherry picked from commit 6e17a2e00d62fd3041e0bb511fe925079ad1c0d7)