fix(yamux): yamux uses wrong direction during dcutr

[diegomrsantos]

During DCUtR, the listener initiates the direct connection attempt and must connect to the other peer as the incoming upgrade direction. Yamux must use this direction to decide on using odd or even stream IDs, not the underlying connection direction -which in this case is TCP (or another transport) outgoing as the peer is initiating the connection.

This is an unusual case where a peer initiates a connection, but should treat it as incoming. The reason is probably that DCUtR happens when the other remote peer dials this peer relayed address, therefore the original connection was in fact incoming.

Related:
https://github.com/libp2p/specs/tree/master/yamux
https://github.com/libp2p/specs/blob/master/relay/DCUtR.md

[codecov]

Codecov Report

Merging #992 (5bd55be) into unstable (ce0685c) will increase coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #992      +/-   ##
============================================
+ Coverage     83.23%   83.25%   +0.01%     
============================================
  Files            91       91              
  Lines         15328    15331       +3     
============================================
+ Hits          12759    12764       +5     
+ Misses         2569     2567       -2     

Files	Coverage Δ
libp2p/builders.nim	93.05% <100.00%> (ø)
libp2p/dialer.nim	92.73% <ø> (-0.04%)	⬇️
libp2p/muxers/muxer.nim	72.00% <ø> (ø)
libp2p/muxers/yamux/yamux.nim	89.72% <100.00%> (+0.03%)	⬆️
libp2p/upgrademngrs/muxedupgrade.nim	87.69% <100.00%> (ø)

... and 2 files with indirect coverage changes

[diegomrsantos]

This is replaced by #994