chan_mgcp: Enforce locking for oseq

This restricts direct usage of global oseq so that all accesses are
locked and threads are not racing to get oseq values that they did not
claim.

This also fixes a build error in res_pktccops under dev mode.

(closes issue ASTERISK-23100)
Reported by: adomjan
Patch by: adomjan


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@406037 f38db490-d61c-443f-a65b-d21fe96a405b
manager: Clarify eventfilter documentation. Textual changes only.

Review: https://reviewboard.asterisk.org/r/3133/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@406079 f38db490-d61c-443f-a65b-d21fe96a405b