vmm: net: Don't kill the VM when failing to bypass

vmm: net: Don't kill the VM when failing to bypass

Previously, if we failed to set up a bypass, we'd kill the VM.
Unfortunately, it's very easy to run out of conversations in Plan 9.  UDP
has 256, TCP has 1024, and the max for a protocol is 4096 - far less than
65K.

Now, instead of dying, we'll print out a warning, but otherwise let the VM
exist.  Once we fix Plan 9's stack, we can consider reverting this.

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>