Revert "Bluetooth: Mesh: Fix ignoring invalid Transport OpCode as LPN"

This reverts commit ada5771d.

MESH/NODE/FRND/LPN/BI-02-C in Mesh Test Specification 1.0.1
has been fixed according to TSE #9774.

IUT shall ignore the message with an RFU Transport Control Opcode
but another Friend Poll message shall be sent with an alternating
FSN value.

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>