src: rename ibrportname, obrportname

src: rename ibrportname, obrportname

For bridge, iifname is the port name, whereas 'ibrport' is the
logical name of the bridge ("br0") the port ("iifname") is enslaved to.

So, 'ibrport' is a misnomer.

libnftl calls these 'bri_iifname' and 'bri_oifname', which is good
but using 'briiifname' in nft is rather ugly, so use 'ibridgename'
and 'obridgename' instead.

Old names are still recognized, listing shows the new names.

Signed-off-by: Florian Westphal <fw@strlen.de>