string_item_to_iaddr: Actually set port if !CONFIG_IPV6

string_item_to_iaddr: Actually set port if !CONFIG_IPV6

This bug was introduced along with this function in bb839899 `Provide
string_item_to_iaddr', which simply forgot to set the port.

The practical implications are that the port number of a locally bound
socket would not be specified, if an address was supplied, but only in
builds without IPv6 support.  (This might result in the kernel picking
a port nmber; if authbind is in use it would probably cause authbind
to refuse.)

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>