wlan: Mark peer as forced peer for TDLS External Configuration

Currently when executing tdls_setup or tdls_discover commands
from userspace as a part of TDLS External configuration the peer
is created in driver but not marked as forced_peer, when trying
to send setup request frame, host driver is checking forced_peer
flag and since it is not marked as forced_peer it is failing.
Similarly for implicit discovery process even when the threshold
is reached since it is not marked as forced_peer implicit
discover is not triggered.
These changes fix the issue by marking peer as forced_peer while
adding peer in driver if External TDLS is configured.

Change-Id: I355a1f1b8644803cfc4e528ea966976e0e4422e8
CRs-fixed: 2897824