drivers: rmnet_perf: Avoid recursive spinlock in legacy mode

Commit 56901a4a6639 ("drivers: rmnet_perf: Take lock during DL marker
handling") locks the DL marker handling to ensure synchronization. When
rmnet_perf handles deaggregation of QMAP frames, this will result in
attempting to take the lock recursively, as the lock will already be held
by the deaggregation logic.

Change-Id: I731574ed56e770193c9b094758d7f4119ef91781
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>