GAP: Correct the continuous pkt length in l2cap

L2cap continuous pkt length wrongly calculated in
reassembly logic when remote sends more data
than expected.

Wrong pkt length leading to memory corruption

Hence the Correct the continuous pkt length in
l2cap reassembly logic.

Bug: 135239489
Bug: 143894715
CRs-Fixed: 2434229
Test: make and internal testing
Change-Id: I758d9e31465b99e436b9b1841320000f08186c97
Merged-In: I758d9e31465b99e436b9b1841320000f08186c97
(cherry picked from commit 2985c8f2)