trx: split TRX ctrl response parsing from socket callback
Extract TRX control response parsing logic into
trx_ctrl_parse_rsp() and call it from trx_ctrl_read_cb()
This decouples parsing from socket I/O and allows reuse
with alternative transports
No functional changes intended
Change-Id: I255c7d554aad3ac6df2c66716fae1c1fb512110e
