tests: bluetooth: tester: Adjust Segment Retransmit Count

In test cases MESH/NODE/TNPT/BV-04-C and MESH/NODE/TNPT/BI-01-C
the PTS is sending incomplete Seg Ack 3 times and in some cases we run
out of retransmit attempts before PTS sends complete Seg Ack. As a
workaround, increase Segment Retransmit Count to improve stability of
these tests.

Signed-off-by: Michał Narajowski <michal.narajowski@codecoup.pl>