cosmetic: move translation of vlr_ciph into msc_vlr_set_ciph_mode()

a_iface_tx_cipher_mode() is a bit too far away from the VLR to be handling its
ciphering enums. Instead, construct the gsm0808_encrypt_info in the
msc_vlr_set_ciph_mode() callback.

Greatly simplify the sanity checking code: a_iface_tx_cipher_mode() no longer
needs to re-verify the presence of the gsm0808_encrypt_info contents.

Change-Id: Id46f9a513b555d0a481f7124c9984c2b5b196b3e
3 files changed