pkg/nimble: fix the event queue size for nimble_adv_ext

[gschorcht]

Contribution description

This PR increases the event queue size to fix a bug if module nimble_adv_ext is used.

If the Bluetooth 5 Advertising Extension is enabled by the nimble_adv_ext module, the 3 events

LE Enhanced Connection Complete event
LE Channel Selection Algorithm event
LE Advertising Set Terminated event

come in from the controller during connection setup before they are processed by the host. The default size of the event queue MYNEWT_VAL_BLE_TRANSPORT_EVT_COUNT with only 2 entries is too small and the LE Advertising Set Terminated event is lost. Therefore, each connection setup fail. Increasing the event queue size MYNEWT_VAL_BLE_TRANSPORT_EVT_COUNT to 4 solves the problem.

The problem was figured out when investigating the problems for tests/nimble_*_ext in PR #18439.

Testing procedure

Flash two nRF52x nodes with

BOARD=nrf52... make -C tests/nimble_autoconn_gnrc_ext/ flash term

an check the results. Without this PR, the connection can't be established and command ble info shows the following results on both nodes

Own Address: F4:4E:D7:67:1B:2A -> [FE80::F44E:D7FF:FE67:1B2A]
Supported PHY modes: 1M 2M CODED
 Free slots: 2/3
Advertising: yes
Connections: 0
Slots:
[ 0] state: 0x0100 - advertising
[ 1] state: 0x8000 - unused
[ 2] state: 0x8000 - unused

With this PR, the connection should be established and command ble info should show the following results.

Node1:

Own Address: F4:4E:D7:67:1B:2A -> [FE80::F44E:D7FF:FE67:1B2A]
Supported PHY modes: 1M 2M CODED
 Free slots: 1/3
Advertising: yes
Connections: 1
[ 0] DD:67:34:05:2D:D6 [FE80::DD67:34FF:FE05:2DD6] (S,75ms,2500ms,0,1M)
     (role, conn itvl, superv. timeout, slave latency, PHY)
Slots:
[ 0] state: 0x0022 - GAP-slave L2CAP-server
[ 1] state: 0x0100 - advertising
[ 2] state: 0x8000 - unused

Node 2:

Own Address: DD:67:34:05:2D:D6 -> [FE80::DD67:34FF:FE05:2DD6]
Supported PHY modes: 1M 2M CODED
 Free slots: 1/3
Advertising: yes
Connections: 1
[ 0] F4:4E:D7:67:1B:2A [FE80::F44E:D7FF:FE67:1B2A] (M,75ms,2500ms,0,1M)
     (role, conn itvl, superv. timeout, slave latency, PHY)
Slots:
[ 0] state: 0x0011 - GAP-master L2CAP-client
[ 1] state: 0x0100 - advertising
[ 2] state: 0x8000 - unused

Issues/PRs references

Prerequisite for PR #18439

[maribu]

I fast-tracked #18466 as all other PRs would fail anyway until that gets merged. Sorry for the delay.

[gschorcht]

Thanks for reviewing and merging.