In change [1] together with the actual implementation I introduced
a serious bug to trx_sched_fn(): if a timeslot is configured to use
frequency hopping, both 'pinst' and 'l1h' pointers are *overwriten*
in the inner loop, so the Downlink burst is re-directed to the
approproate PHY instance. However, if a subsequent timeslot is not
hopping, the Downlink burst would be re-directed to the wrong PHY
instance because both pointers were overwriten during a previous
iteration.
Let's add another 'struct phy_instance' pointer to the inner loop,
so it's properly re-initialized for each timeslot iteration.
Change-Id: I9afbbef8dc5d885763356470c27d4392dce8e815
Fixes: [1] I68f4ae09fd0789ad0d8f1c1e17e17dfc4de8e462
Related: SYS#4868, OS#4546