Bluetooth: assertion fail with basic repeated extended advertisement API

[pabigot]

The head commit on https://github.com/pabigot/zephyr/tree/testing/extadv modifies the beacon sample to use extended advertising to control the frequency of advertisements. It creates an advertising set, configures it for one transmission, then after the transmission completes schedules another transmission five seconds later.

The program aborts with the following error after the fifth transmission completes.

ASSERTION FAIL [delta <= 0 || mem_link_rx.quota_pdu < ((1 + 3) + 2)] @ WEST_TOPDIR/zephyr/subsys/bluetooth/controller/ll_sw
/ull.c:1047
[00:00:20.298,889] <err> os: r0/a1:  0x00000003  r1/a2:  0x0000000a  r2/a3:  0x00000000
[00:00:20.298,889] <err> os: r3/a4:  0x00001c15 r12/ip:  0x00000000 r14/lr:  0x00005f2d
[00:00:20.298,889] <err> os:  xpsr:  0x61000000
[00:00:20.298,919] <err> os: Faulting instruction address (r15/pc): 0x00005f38
[00:00:20.298,919] <err> os: >>> ZEPHYR FATAL ERROR 3: Kernel oops on CPU 0
[00:00:20.298,919] <err> os: Current thread: 0x20000690 (unknown)
[00:00:20.344,268] <err> os: Halting system

Analysis shows that the increment at https://github.com/zephyrproject-rtos/zephyr/blob/master/subsys/bluetooth/controller/ll_sw/ull.c#L984 is not paired with a decrement anywhere, when processing a link node of type NODE_RX_TYPE_EXT_ADV_TERMINATE.