Improve active_tcp test timeout

Deprecate AgentConfig

Cancel gathering before removing candidates (#842)

#### Description

When ICE agent is closed, the connections from UDP/TCP mux were removed
before gathering was canceled. This led to candidate gathering adding
entries to UDP mux which were not cleaned up.

~Also passing into logger to the mux as ICE agent logger could have more
context and is useful to see the context.~

Set linger time for tcp connections (#841)

#### Description

It is possible that Close() of a TCP connection to block if there is
pending data to be written till it is written out. Set linger to ensure
that it does not block.

Fix a deadlock in TaskLoop

Implement ICE Role conflict resolution

Detect if remote has a role conflict and resolve it as defined by
RFC 8445 section-7.3.1.1

Resolves #359

Pass LoggerFactory to dtls and mdns (#772)

Handle candidate: prefix with UnmarshalCandidate

Make UnmarshalCandidate able to handle candidate: prefix in the
candidate string.

Always send KeepAlives (#767)

Pion incorrectly resets the consent timer when sending any traffic. 
The consent timer must only be reset on STUN traffic.

RFC 7675
> Consent expires after 30 seconds.  That is, if a valid STUN binding
> response has not been received from the remote peer's transport
> address in 30 seconds, the endpoint MUST cease transmission on that
> 5-tuple.  STUN consent responses received after consent expiry do not
> re-establish consent and may be discarded or cause an ICMP error.

Add Req/Res count/time to candidate stats (#763)

These details will provide information for
connectivity issue.