Changes

bts: Fix sporadic failure in TC_rsl_ms_pwr_ctrl

Fix following sporadic race condition:
TTCN-MS         IUTS-BTS           TTCN-BSC
   |              |<----CHAN_ACT------|
   |<--SACCH(A)-- |                   |
   |              |<--MS_PWR_CTRL(B)- |
   |<--SACCH(B)---|

Change-Id: I088b58bf76765c8a5bd167590c5afc5055fbdbf8