Bluetooth: controller: ASSERTION FAIL Radio is on during flash operation

[cvinayak]

Describe the bug
Flash operations on nrf52840_pca10056 tests/bluetooth/shell raises ASSERTION FAIL.

To Reproduce
Steps to reproduce the behavior:

1. mkdir build; cd build
2. cmake -DBOARD=nrf52840_pca10056 ../tests/bluetooth/shell
3. make
4. See error

Expected behavior
There shall be no assertion and flash operations succeed.

Impact
showstopper

Screenshots or console output

uart:~$ bt init
Bluetooth initialized
uart:~$ bt[00:00:03.854,278] <inf> fs_nvs: 8 Sectors of 4096 bytes
[00:00:03.854,309] <inf> fs_nvs: alloc wra: 1, fc0
[00:00:03.854,309] <inf> fs_nvs: data wra: 1, 34
[00:00:03.857,086] <inf> bt_hci_core: HW Platform: Nordic Semiconductor (0x0002)
[00:00:03.857,086] <inf> bt_hci_core: HW Variant: nRF52x (0x0002)
[00:00:03.857,086] <inf> bt_hci_core: Firmware: Standard Bluetooth controller (0x00) Version 2.2 Build 0
[00:00:03.857,666] <inf> bt_hci_core: No ID address. App must call settings_load()
[00:00:03.868,041] <inf> bt_hci_core: Identity: ea:c8:5c:41:6e:de (random)
[00:00:03.868] <inf> bt_hci_core: LMP: version 5.1 (0x0a) subver 0xffff
...
...
uart:~$ bt connect 62:aa:1d:d4:2a:de (random)
Connection pending
Connected: 62:aa:1d:d4:2a:de (random)
Remote LMP version 5.1 (0x0a) subversion 0xffff manufacturer 0x05f1
LE Features: 0x000000000001417f 
[00:00:22.419,464] <inf> bt_hci_core: PHY updated (0x0): status: 0x00, tx: 2, rx: 2
[00:00:22.429,077] <inf> bt_hci_core: Data Length (0x0): max. tx: 27 (328us), max. rx: 27 (164us)
[00:00:22.436,584] <inf> bt_hci_core: Data Length (0x0): max. tx: 27 (328us), max. rx: 27 (328us)
LE conn  param req: int (0x0018, 0x0028) lat 0 to 42
LE conn param updated: int 0x0028 lat 0 to 42
...
...
uart:~$ bt conn-update 6 6 0 64
conn update initiated.
LE conn param updated: int 0x0006 lat 0 to 100
uart:~$ 
...
...
uart:~$ flash test 0xf8000 0x1000 100
Erase OK.
Write OK.
...
...
Erase OK.
Write OK.
ASSERTION FAIL [ll_radio_state_is_idle()] @ ZEPHYR_BASE/drivers/flash/soc_flash_nrf.c:287
        Radio is on during flash operation.

ASSERTION FAIL [!arch_is_in_isr()] @ ../../kernel/include/ksched.h:262

ASSERTION FAIL [!arch_is_in_isr()] @ ../../kernel/include/ksched.h:262

Environment (please complete the following information):

• OS: Linux
• Toolchain: Zephyr SDK 0.11.1
• Commit SHA or Version used: a9bfd28

Additional context
Add any other context about the problem here. None.