use BSC_FD_READ and not OSMO_FD_READ
use BSC_FD_READ and not OSMO_FD_READ

We haven't even released any tagged version of libosmocore yet which
includes support for the renamed OSMO_FD_READ constant.  Let's avoid
any breakage and use the new constants only with considerable delay,
at the very least only when released libosmocore versions provide it.

Change-Id: Idb57077b2a4b2a71dd5d75a24ded8bb5887da188

osmocom/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx