res_pjsip: Make transport cipher option accept a comma separated list of cipher names.

Improvements to the res_pjsip transport cipher option.

* Made the cipher option accept a comma separated list of OpenSSL cipher
names.  Users of realtime will be glad if they have more than one name to
list.

* Added the CLI command 'pjsip list ciphers' so a user can know what
OpenSSL names are available for the cipher option.

* Updated the cipher option online XML documentation to specify what is
expected for the value.

* Updated pjsip.conf.sample to not indicate that ALL is acceptable since
ALL does not imply a preference order for the ciphers and PJSIP does not
simply pass the string to OpenSSL for interpretation.

ASTERISK-24199 #close
Reported by: Joshua Colp

Review: https://reviewboard.asterisk.org/r/4018/
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Merged revisions 424393 from http://svn.asterisk.org/svn/asterisk/branches/12
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Merged revisions 424394 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@424395 65c4cc65-6c06-0410-ace0-fbb531ad65f3