Previously, the L1CTL_CRYPTO_REQ message contained only a ciphering
algorithm and actual Kc key to be used. The key length was
calculated manually using the MSGB API.
Let's avoid manual calculations here, as it may cause unexpected
behavior if the message structure is changed. Also, let's fill
the UL header with minimal information about a channel, which
is going to be encrypted.
Change-Id: I1813a188e755141241273479b17896415abcc3f1
255f25ef25