block/gluster: fix port type in the QAPI options list

block/gluster: fix port type in the QAPI options list

After introduction of qapi schema in gluster block driver code, the port
type is now string as per InetSocketAddress

{ 'struct': 'InetSocketAddress',
  'data': {
    'host': 'str',
    'port': 'str',
    '*to': 'uint16',
    '*ipv4': 'bool',
    '*ipv6': 'bool' } }

but the current code still treats it as QEMU_OPT_NUMBER, hence fixing port
to accept QEMU_OPT_STRING.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>