bluetooth: host: Add a check for num of bt_conn_tx and ACL/ISO bufs

After https://github.com/zephyrproject-rtos/zephyr/pull/72090

, each
packet to be sent (wether ACL or ISO data) has a corresponding
`bt_conn_tx` object, regardless of whether a callback is used.

This means that number of packets Host can send to Controller is limited
by the smaller of two values: ACL/ISO packets Controller can receive,
and the number of `bt_conn_tx` objects allocated by Host.

A mismatch between these numbers may lead to inefficient resource usage
on either Host or Controller side. If Host allocates fewer `bt_conn_tx`
objects than the number of buffers available on Controller for a given
data type, some Controller buffers may go unused. Conversely, if Host
allocates more `bt_conn_tx` objects than Controller can consume, the
excess objects remain unused.

This commit adds a check and issues a warning if the number of
`bt_conn_tx` objects is not aligned with the number of ACL/ISO buffers
reported by Controller via the LE Read Buffer Size v1 or v2 command.

Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>