Increment seq before adding to packet in avdt_scb_hdl_write_req_no_frag

Bluetooth Certification Test case TP/TRA/BTR/BV-01-C for Basic
Transport Service Support fails. The failure is because the PTS
is expecting the first RTP Media Frame to have a sequence number
of 1. But metallica sends it as 0.
bug 17893538

Change-Id: Idfe7ae382c3764616dab4733cdf83b1627b8b3c9