Fix Radio Priority in MM Attach and PDP Context Activation
3GPP TS 24.008 Section 10.5.7.2 Radio Priority states that the Radio Priority IE is
3 bits as follows:
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0 0 1 priority level 1 (highest)
0 1 0 priority level 2
0 1 1 priority level 3
1 0 0 priority level 4 (lowest)
All other values are interpreted as priority
level 4 by this version of the protocol.
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However at least the MediaTek MT6753 and MT6592 have been
observed to interpret a value of 0 0 0 in an undetermined way
resulting in lack of access to RACH in the cell.
Fixes: OS#4506
Change-Id: I810cd541eb5764ee3f2c238bcd3a10836228d0b5