osmo-bts-omldummy: indicate BTS_FEAT_BCCH_POWER_RED as supported
osmo-bts-omldummy: indicate BTS_FEAT_BCCH_POWER_RED as supported

This is required for ttcn3-bsc-test, see change [1].

Change-Id: I765d5e38cb0746e0458773abf3717ee9bf1cb7d1
Related: [1] I084f7736cd7d09b68ed49f8ba52a14de928d4c01
Related: SYS#4919

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