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

void btpan_set_flow_control(BOOLEAN enable) {
 if (btpan_cb.tap_fd == -1)
 return;

    btpan_cb.flow = enable;
 if (enable) {
        btsock_thread_add_fd(pan_pth, btpan_cb.tap_fd, 0, SOCK_THREAD_FD_RD, 0);
        bta_dmexecutecallback(btu_exec_tap_fd_read, (void *)btpan_cb.tap_fd);
 }
}

void btpan_set_flow_control(BOOLEAN enable) {
 if (btpan_cb.tap_fd == -1)
 return;

    btpan_cb.flow = enable;
 if (enable) {
        btsock_thread_add_fd(pan_pth, btpan_cb.tap_fd, 0, SOCK_THREAD_FD_RD, 0);
        bta_dmexecutecallback(btu_exec_tap_fd_read, (void *)btpan_cb.tap_fd);
 }
}
