nimble/phy/nrf5x: Fix tx-tx transition
nimble/phy/nrf5x: Fix tx-tx transition

We need to store current transition before calling txend callback. This
is important in case of tx-tx transition since txend callback will call
ble_phy_tx which overwrites current transition.

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble