osmo-bts-trx: rx_tchh_fn(): fix HR SID detection (wrong offset)
osmo-bts-trx: rx_tchh_fn(): fix HR SID detection (wrong offset)

According to RFC5993, which is referenced by 3GPP TS 48.103, the
complete RTP HR payload consists of a Table-of-Contents (ToC) byte
followed by the 14 bytes of the HR codec frame.  See section 5.2.

gsm0503_tch_hr_decode() outputs frames in the RTP format with
length of 15 bytes (120 bits): 1 (ToC) + 14 (HR frame):

  +-------------+-------------------------
  | ToC section | HR codec frame ...
  +-------------+-------------------------

osmo_hr_check_sid() expects a HR codec frame of 14 bytes (112 bits)
as the input, so we should skip the ToC section when calling it.

Change-Id: Ie5fa776dcb2b2203a97aed56ecbf2450af7d87c1
Related: SYS#5853

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts