power_ctrl_params_def_reset(): set .ctrl_interval for both UL/DL
power_ctrl_params_def_reset(): set .ctrl_interval for both UL/DL

For the sake of consistency and code readability, initialize the
power loop control interval (P_Con_INTERVAL) for both Uplink and
Downlink directions in the same function.

Change-Id: If7c804e51eb104d9fe73294a3867ab3b551d83c3

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