write_sdu and write_pdu are not re-entrant because all functions
that deal with the counters, e.g. integrity check and generate,
must be protected because MAC threads may call them at the same time.
this addresses issue #254
This is a larger patch that reworks the LCID handling throughout the
code.
- It first moves the RB/LCID mapping out of common.h into the RRC object
because different RATs may have different mappings.
- It adds a interface to RRC that other objects like RLC/PDCP/etc. may
use to get the bearer name of a specific LCID.
- The patch also introduces a PDCP config class.