Add note to the install doc about bridge MAC issues
Add note to the install doc about bridge MAC issues

Thanks to Faidon Liambotis for explaining this on the external IRC
channel.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Faidon Liambotis <b5f297ae1db97129134ea299877e232142939f36@gmail.com>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>

apyrgio/snf-ganeti,apyrgio/ganeti,yiannist/ganeti,andir/ganeti,onponomarev/ganeti,leshchevds/ganeti,grnet/snf-ganeti,apyrgio/ganeti,bitemyapp/ganeti,ganeti/ganeti,onponomarev/ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,bitemyapp/ganeti,andir/ganeti,apyrgio/snf-ganeti,ganeti/ganeti,mbakke/ganeti,leshchevds/ganeti,dimara/ganeti,ganeti/ganeti,mbakke/ganeti,yiannist/ganeti,andir/ganeti,dimara/ganeti,mbakke/ganeti,yiannist/ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1