network: fix crash during cleanup from failure to allocate port

network: fix crash during cleanup from failure to allocate port

During networkPortCreateXML, if networkAllocatePort() failed,
networkReleasePort() would be called, which would (in the case of
network pools of macvtap passthrough devices) attempt to find the
allocated device by comparing port->plug.direct.linkdev to each device
in the pool. Since port->plug.direct.linkdev was still NULL, the
attempted strcmp would result in a SEGV.

Calling networkReleasePort() during error cleanup is something that
should only be done if networkAllocatePort() has already succeeded. It
turns out there is one other possible error exit from
networkPortCreateXML() that happens after networkAllocatePort() has
succeeded, so the code to call networkReleasePort() was just moved
down to there.

Resolves: https://bugzilla.redhat.com/1741390

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>