Fix warnings on 64 bit platforms.
Fix warnings on 64 bit platforms.

yarrcc/libsrtp-ios,yarrcc/libsrtp-ios,cuijinquan/libsrtp,persmule/libsrtp,persmule/libsrtp,ksophocleous/libsrtp,ksophocleous/libsrtp,Distrotech/libsrtp,persmule/libsrtp,yarrcc/libsrtp-ios,Distrotech/libsrtp,cuijinquan/libsrtp,cuijinquan/libsrtp