Relaying doesn't work when TCPOnly is enabled

[DDoSolitary]

Assume the following topology:
A <--> B <--> C
(A and C are behind firewalls and can only establish direct TCP connection with B)

If I set TCPOnly = yes for node C, B will drop packets sent from A to C, while all other situations work properly (B to C, C to B, and even C to A)
If I leave TCPOnly = no, even though only TCP connections are available (as UDP packets will be dropped by firewalls), everything works as expected.

After some digging, I found that TCPOnly enabled nodes will never have the validkey status flag set, and packets indirectly targeting C are dropped by B from here: 2c9126a
If I revert the commit everything works again, but I'm not sure if it's the correct way to fix the problem, or there's something wrong elsewhere resulting in validkey unset.