AES key size is restricted to block size (16)

[abedra]

https://github.com/hashicorp/vault/blob/master/vault/barrier_aes_gcm.go#L70-L73

This restricts the encryption to 128. A key size of 256 bits is perfectly acceptable as well. Is there a reason why it is restricted this way?

[armon]

@abedra Good catch! I've allowed both 128 and 256 now and changed the default to 256.

[abedra]

Thanks!