Fix all linting errors

Disabled gocylco for now, need to use gometalinter to disable
conditionally. There are also a lot more linters we could use, but they
cause too many issues to start today.

internal/sdp/unmarshal.go

@@ -112,7 +112,6 @@ func (s *SessionDescription) Unmarshal(raw string) error {
 	return s.unmarshalOptionalAttributes(scanner)
 }
 
-// nolint: gocyclo
 func (s *SessionDescription) unmarshalOptionalAttributes(scanner *bufio.Scanner) error {
 	orderedSessionAttributes := []*attributeStatus{
 		{value: "v"},