OBEX: Reduce Obex MTU size for A2DP or SCO concurrency

Reduce Obex MTU to 8k from 64k when OPP send is tried with
SCO / A2DP streaming in progress, so that the continue
response for first complete Obex PUT packet is received
from SOC within 50 seconds time frame.

CRs-Fixed: 571865
Change-Id: I1eae114f57f2a92ee4b26c82d8f55fafe02775b8