conn: windows: do not error out when receiving UDP jumbogram

conn: windows: do not error out when receiving UDP jumbogram

If we receive a large UDP packet, don't return an error to receive.go,
which then terminates the receive loop. Instead, simply retry.

Considering Winsock's general finickiness, we might consider other
places where an attacker on the wire can generate error conditions like
this.

Reported-by: Sascha Dierberg <sascha.dierberg@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>