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