aesni(4): Fix {de,en}crypt operations that allocated a buffer

aesni(4) allocates a contiguous buffer for the data it processes if the
provided input was not already virtually contiguous, and copies the input
there. It performs encryption or decryption in-place.

r324037 removed the logic that then copied the processed data back to the
user-provided input buffer, breaking {de,enc}crypt for mbuf chains or
iovecs with more than a single descriptor.

PR: 228094 (probably, not confirmed)
Submitted by: Sean Fagan <kithrup AT me.com>
Reported by: Emeric POUPON <emeric.poupon AT stormshield.eu>
X-MFC-With: 324037
Security: could result in plaintext being output by "encrypt"

		operation