Bluetooth: controller: LEGACY: ASSERTION failure on invalid packet sequence

[cvinayak]

Describe the bug
A rough central device using invalid sequence number in the first connection event causes assertion failure in the controller.

To Reproduce
Steps to reproduce the behavior:

1. mkdir build; cd build
2. cmake -DBOARD=nrf52_pca10040 -DCONFIG_BT_LL_SW_LEGACY=y ../samples/bluetooth/peripheral
3. make
4. See error

Expected behavior
No assertion failure or crash.

Impact
showstopper

Screenshots or console output

*** Booting Zephyr OS build v2.2.0-rc1-215-g6baff1b3b9c0  ***
Bluetooth initialized
Advertising successfully started
[00:00:00.007,476] <inf> fs_nvs: 6 Sectors of 4096 bytes
[00:00:00.007,476] <inf> fs_nvs: alloc wra: 0, fa8
[00:00:00.007,476] <inf> fs_nvs: data wra: 0, e4
[00:00:00.008,880] <inf> bt_hci_core: HW Platform: Nordic Semiconductor (0x0002)
[00:00:00.008,880] <inf> bt_hci_core: HW Variant: nRF52x (0x0002)
[00:00:00.008,880] <inf> bt_hci_core: Firmware: Standard Bluetooth controller (0x00) Version 2.2 Build 0
[00:00:00.009,155] <inf> bt_hci_core: No ID address. App must call settings_load()
[00:00:00.011,901] <inf> bt_hci_core: Identity: c1:ab:66:13:11:2e (random)
[00:00:00.011,932] <inf> bt_hci_core: HCI: version 5.1 (0x0a) revision 0x0000, manufacturer 0x05f1
[00:00:00.011,932] <inf> bt_hci_core: LMP: version 5.1 (0x0a) subver 0xffff
Connected
ASSERTION FAIL [status == 0] @ ZEPHYR_BASE/subsys/bluetooth/controller/ll_sw/ctrl.c:5050
[00:00:15.125,396] <err> os: r0/a1:  0x00000003  r1/a2:  0x0000000a  r2/a3:  0x00000001
[00:00:15.125,427] <err> os: r3/a4:  0x000204d2 r12/ip:  0x200010cc r14/lr:  0x00011a5b
[00:00:15.125,427] <err> os:  xpsr:  0x61000029
[00:00:15.125,427] <err> os: Faulting instruction address (r15/pc): 0x00011a66
[00:00:15.125,427] <err> os: >>> ZEPHYR FATAL ERROR 3: Kernel oops on CPU 0
[00:00:15.125,427] <err> os: Fault during interrupt handling

[00:00:15.125,427] <err> os: Current thread: 0x2000183c (unknown)
[00:00:15.438,201] <err> os: Halting system

Environment (please complete the following information):

• OS: Linux
• Toolchain: gnuarmemb gcc version 9.2.0 (Arch Repository)
• Commit SHA or Version used: 6baff1b

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