dcb: add new pcp-prio parameter to dcb app

dcb: add new pcp-prio parameter to dcb app

Add new pcp-prio parameter to the app subcommand, which can be used to
classify traffic based on PCP and DEI from the VLAN header. PCP and DEI
is specified in a combination of numerical and symbolic form, where 'de'
(drop-eligible) means DEI=1 and 'nd' (not-drop-eligible) means DEI=0.

Map PCP 1 and DEI 0 to priority 1
$ dcb app add dev eth0 pcp-prio 1nd:1

Map PCP 1 and DEI 1 to priority 1
$ dcb app add dev eth0 pcp-prio 1de:1

Internally, PCP and DEI is encoded in the protocol field of the dcb_app
struct. Each combination of PCP and DEI maps to a priority, thus needing
a range of  0-15. A well formed dcb_app entry for PCP/DEI
prioritization, could look like:

    struct dcb_app pcp = {
        .selector = DCB_APP_SEL_PCP,
	.priority = 7,
        .protocol = 15
    }

For mapping PCP=7 and DEI=1 to Prio=7.

Also, three helper functions for translating between std and non-std APP
selectors, have been added to dcb_app.c and exposed through dcb.h.

Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>