mesh: Avoid use of hardcoded cipher

mesh: Avoid use of hardcoded cipher

This moves pairwise, group, and management group ciphers to various mesh
data structures to avoid having to hardcode cipher in number of places
through the code. While CCMP and BIP are still the hardcoded ciphers,
these are now set only in one location.

Signed-off-by: Jouni Malinen <j@w1.fi>