Bluetooth: controller: llcp: limited nr. of simultaneous connections

[kruithofa]

Describe the bug
the babblesim test tests/bluetooth/bsim_bt/bsim_test_multiple fails if the maximum number of connections is higher than circa 170.
The test should pass with a maximum number of connections set to 250

To Reproduce

1. change the prj.conf file, so that CONFIG_BT_MAX_CONN=250
2. run the script 'compile.sh' or alternatively only compile the bsim_test_multiple sample
3. run the script tests/bluetooth/bsim_bt/bsim_test_multiple/test_scripts/multiple.sh
4. there will be error-messages saying that connecting failed after about 170 succesfull connections

Possible cause might be related to the allocated buffers, using an uint8_t instead of uint16_t causing memory corruption

[kruithofa]

This may be fixed by a coming PR from @erbr-ot , to be verified when this PR is available.
Verified that this issue is more complex