add support for bareudp link type

[bersoare]

this PR adds support for bareudp link attributes.

2 links with similar attributes - one created using this code, another one using iproute2:

13: bareudp1: <POINTOPOINT,MULTICAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/none  promiscuity 0 minmtu 68 maxmtu 65527
    bareudp dstport 6636 ethertype mpls_uc srcportmin 12345 multiproto addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
14: foo99: <POINTOPOINT,MULTICAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default
    link/none  promiscuity 0 minmtu 68 maxmtu 65527
    bareudp dstport 6635 ethertype mpls_uc srcportmin 12345 multiproto addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535

[aboch]

LGTM

But I we need to wait for @vishvananda to see if he can revive Travis CI integration

[aboch]

Please rebase and force-push so that CI (now fixed) is triggered

[aboch]

LGTM