bgpd: add l2vpn evpn to afi safi parse utility

bgpd: add l2vpn evpn to afi safi parse utility

Problem reported with "clear bgp l2vpn evpn * soft" clearing the
wrong afi/safi (cleared ipv6 unicast instead).  Determined that
the calling function used the argv_find_and_parse_afi/safi routines
to determine the correct afi/safi to pass on.  Since l2vpn/evpn were
missing from the lookup, the command defaulted to ipv6 unicast.  This
fix just adds that afi/safi to the lookup routine.

Ticket: CM-25167
Signed-off-by: Don Slice <dslice@cumulusnetworks.com>