DO NOT MERGE Fix potential DoS caused by delivering signal to BT process

Bug: 28885210
Change-Id: I63866d894bfca47464d6e42e3fb0357c4f94d360

 Conflicts:
	btif/co/bta_hh_co.c
	btif/src/btif_core.c
Merge conflict resolution of ag/1161415 (referencing ag/1164670)
- Directly into mnc-mr2-release

static rfc_slot_t *find_free_slot(void) {
 for (size_t i = 0; i < ARRAY_SIZE(rfc_slots); ++i)
 if (rfc_slots[i].fd == INVALID_FD)
 return &rfc_slots[i];
 return NULL;
}

static rfc_slot_t *find_free_slot(void) {
 for (size_t i = 0; i < ARRAY_SIZE(rfc_slots); ++i)
 if (rfc_slots[i].fd == INVALID_FD)
 return &rfc_slots[i];
 return NULL;
}
