Revert "mrp: LVATIMER event, upon tx_request, perform TX before sLA (fixes always sending NEW)"

This reverts commit e783295adb9d09fff35c1555309326511655a3b4.
Revert "mrp: changes to LVA_TIMER event handling"

This reverts commit 1be29bd145d3bae55a5c926c6f6653398db628a0.
mrp: mrp_lvatimer_fsm(), set tx flag when MRP_EVENT_LVATIMER occurs.

This patch fixes a bug where pdus were being sent from LVATIMER event
without the LeaveAll flag being set.