Update ZRTP interface to use libzrtpcpp min version 4.0.0
- libzrtpcpp v4.0.0 can be compiled in standalone crypto mode
- fix error/warning messages from libzrtpcpp reported by oRTP

Warning: this version of libzrtpcpp have a conflict with libsrtp
with aes_encrypt defined by both. Use the libsrtp version from
linphone repository to get them working together.