Bluetooth: controller: llcp: avoid regression errors

The change in this commit is required to avoid regression errors
on EBQ test for the PHY update procedure
When in the peripheral role transmission of data must be resumed
while waiting for the PHY IND response from peer.
In other words: in the LP_PU_STATE_WAIT_TX_ACK_PHY_REQ state
data transmission must resume when acting as peripheral,
but not when in the central role

Following tests are effected
LL/CON/PER/BV-49-C
LL/CON/PER/BV-50-C
LL/CON/PER/BV-52-C
LL/CON/PER/BV-53-C
LL/CON/PER/BV-54-C
LL/CON/PER/BV-55-C
LL/CON/PER/BV-56-C
LL/CON/PER/BV-58-C

Signed-off-by: Andries Kruithof <andries.kruithof@nordicsemi.no>
(cherry picked from commit 1d1a2f8b)