Bluetooth: controller: llcp: Fix data pause/resume

llcp_tx_pause_data() calls ull_tx_q_pause_data() for each pause_mask,
while llcp_tx_resume_data() only calls ull_tx_q_resume_data() when
conn->llcp.tx_q_pause_data_mask == 0 leading to an unbalanced number of
calls to ull_tx_q_pause_data()/ull_tx_q_resume_data() which can leave
the data path of the TX Q paused.

Fix such that only the first call to llcp_tx_pause_data() will pause the
data path of the TX Q.

Add unit test to verify correct pause/resume behavior.

Signed-off-by: Thomas Ebert Hansen <thoh@oticon.com>
(cherry picked from commit 154d67d9)