scripts: west_commands: runners: fix support for JLink RTT

JLink refuses new RTT telnet connections for a few moments after a socket
closes. This causes an issue when using `nc` as the telnet viewer, since
JLink would deny the connection. To resolve this, keep the "ping" socket
we use to determine if the RTT viewer is active connected, and use that
socket for RTT communication.

Signed-off-by: Daniel DeGrasse <ddegrasse@tenstorrent.com>