Fix skinny_codec_pref_remove (related to revision #5280 / #5282)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5284 43c1dc8c-776e-4df2-8ef1-6e829299be21
Fix skinny_codec_pref_remove

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5285 43c1dc8c-776e-4df2-8ef1-6e829299be21
Remove skinny_codec_mask from sccp_parse_allow_disallow, as it was not used anymore anyway

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5286 43c1dc8c-776e-4df2-8ef1-6e829299be21
Added comment about inserting / appending behaviour (re-activated append behaviour, to conform to previous implementation)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5287 43c1dc8c-776e-4df2-8ef1-6e829299be21