Ensure (by mutex) that only one "stunnel restart" runs at a time

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Xapi_http: don't retry binding if kernel does not support protocol

In other words: do not waste time retrying binding to an IPv6 address
if the kernel does not support IPv6.

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Merge pull request #1158 from robhoes/mgmt-cw

CLEARWATER: Management interface improvements