Break out internal/net/udp

Breaking out the UDP wrapper to make it re-
usable in pion/sctp.

Relates to pion/sctp#74

go.mod

@@ -3,6 +3,7 @@ module github.com/pion/dtls/v2
 require (
 	github.com/pion/logging v0.2.2
 	github.com/pion/transport v0.10.0
+	github.com/pion/udp v0.0.0-20200620185302-adf622c7c621
 	golang.org/x/crypto v0.0.0-20200602180216-279210d13fed
 	golang.org/x/net v0.0.0-20200602114024-627f9648deb9
 	golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543

go.sum

@@ -4,6 +4,8 @@ github.com/pion/logging v0.2.2 h1:M9+AIj/+pxNsDfAT64+MAVgJO0rsyLnoJKCqf//DoeY=
 github.com/pion/logging v0.2.2/go.mod h1:k0/tDVsRCX2Mb2ZEmTqNa7CWsQPc+YYCB7Q+5pahoms=
 github.com/pion/transport v0.10.0 h1:9M12BSneJm6ggGhJyWpDveFOstJsTiQjkLf4M44rm80=
 github.com/pion/transport v0.10.0/go.mod h1:BnHnUipd0rZQyTVB2SBGojFHT9CBt5C5TcsJSQGkvSE=
+github.com/pion/udp v0.0.0-20200620185302-adf622c7c621 h1:xJ6MZFVO/WFB09IhugZl7IKKDOzOMg7dDDjbS0gQ3tY=
+github.com/pion/udp v0.0.0-20200620185302-adf622c7c621/go.mod h1:BPELIjbwE9PRbd/zxI/KYBnbo7B6+oA6YuEaNE8lths=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=

listener.go

@@ -3,7 +3,7 @@ package dtls
 import (
 	"net"
 
-	"github.com/pion/dtls/v2/internal/net/udp"
+	"github.com/pion/udp"
 )
 
 // Listen creates a DTLS listener