Touch-up error-message and godoc for ConfigVXLANUDPPort
Touch-up error-message and godoc for ConfigVXLANUDPPort

Minor changes following review of the engine pull request
for this feature;

- Remove the name of the function from the error message
  as it's not a debug message.
- Add the valid range to the error message, so that a
  user has sufficient information to address the problem.
- Update GoDoc for the function to describe the default
  port, and valid port-ranges.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

nawawi/docker,Ramzec/docker,docker/docker,thaJeztah/docker,paralin/docker,docker/docker,yosifkit/docker,AkihiroSuda/docker,AkihiroSuda/docker,konstruktoid/docker-upstream,yosifkit/docker,Mokolea/docker,Ramzec/docker,djs55/docker,konstruktoid/docker-upstream,nalind/docker,vdemeester/docker,paralin/docker,cpuguy83/docker,konstruktoid/docker-upstream,mahak/docker,moby/moby,moul/docker,djs55/docker,gnailuy/docker,moby/moby,moby/moby,Mokolea/docker,nawawi/docker,docker/docker,vdemeester/docker,Ramzec/docker,Mokolea/docker,trebonian/docker,paralin/docker,nalind/docker,thaJeztah/docker,jimjag/docker,gnailuy/docker,mahak/docker,jameszhan/docker,bearstech/moby,konstruktoid/docker-upstream,trebonian/docker,gnailuy/docker,nalind/docker,AkihiroSuda/docker,cpuguy83/docker,gnailuy/docker,paralin/docker,jameszhan/docker,Mokolea/docker,vdemeester/docker,djs55/docker,mahak/docker,flavio/docker,nawawi/docker,thaJeztah/docker,moul/docker,bearstech/moby,nalind/docker,nawawi/docker,thaJeztah/docker,jthelin/docker,flavio/docker,flavio/docker,jimjag/docker,yosifkit/docker,Ramzec/docker,bearstech/moby,yosifkit/docker,moul/docker,moul/docker,cpuguy83/docker,flavio/docker,moby/moby,jthelin/docker,bearstech/moby,trebonian/docker,cpuguy83/docker,AkihiroSuda/docker,mahak/docker,jimjag/docker,trebonian/docker,jameszhan/docker,jimjag/docker