devlink: Add 'mirror' trap action

devlink: Add 'mirror' trap action

Allow setting 'mirror' trap action for traps that support it. Extend the
devlink-trap man page and bash completion accordingly.

Example:

# devlink -jp trap show netdevsim/netdevsim10 trap igmp_query
{
    "trap": {
        "netdevsim/netdevsim10": [ {
                "name": "igmp_query",
                "type": "control",
                "generic": true,
                "action": "mirror",
                "group": "mc_snooping"
            } ]
    }
}

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>