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/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@424393 f38db490-d61c-443f-a65b-d21fe96a405b