bridge: fdb: rename some variables to contain 'brport'

bridge: fdb: rename some variables to contain 'brport'

Currently, the flush command supports the keyword 'brport'. To handle
this argument the variables 'port_ifidx' and 'port' are used.

A following patch will add support for 'port' keyword in flush command,
rename the existing variables to include 'brport' prefix, so then it
will be clear that they are used to parse 'brport' argument.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David Ahern <dsahern@kernel.org>