Eliminate recursive calling when handling GATT related errors

If there are errors when processing GATT related events (e.g.,
configuring the MTU), don't use recursive calls into
bta_gattc_sm_execute(), because it breaks the free-ing of some
of the memory.

Bug: 23756301
Change-Id: I3c685170e868ffbf4e488d2bb5a31904e3f7b39d