In the past we used to set this to "-10 dBm" which means that basically
no RACH ever passed that treshold and in the associated CCCH LOAD IND
the number of busy slots was always zero.
Let's set the default to -90dBm. The user can of course always
configure a different value in the VTY.
This means that now any RACH slot signal level >= 90 dBm counts as
"busy" in those CCCH LOAD IND (RACH).
Change-Id: Ib9cbb786d19acc74f0951930b0dc9284854c6000
Closes: OS#3004
Related: OS#3003