rlc: Manage the received block bitmap in the ul_window

Added two methods to gprs_rlc_ul_window
* ssn() returns the starting sequence number
* update_rbb() returns an array of chars representing the state of the
  received   block bitmap. Each element is either 'I'nvalid or
  'R'eceived. The rbb is generated from v_n

rbb[63] relates to BSN ssn-1
...
rbb[0] relates to BSN ssn-64
2 files changed