Bluetooth: Getbuf returning invalid buffer pointer - do not merge

Getbuff is checking for the pool which can accommodate
requested size, but is changing the pool with a restricted
check and not checking for the free memory size in that pool.
Added a check to avoid returng the wrong pool free buf pointer.
Without this patch, SDP Codenomicon TestSuite crash is observed
on Bluedroid stack.

Change-Id: Id66d460c5a40d8c3208438d7cfaf729e9b355184