fix wtp_addr_compare

corretly handle the return of the SOCK_ADDR_CMP macro
handle read error correctly and remove the WTP
reduce the required DTLS security level

This is a debug proxy, so 612 bit DH primes are fine, also accept all and
any certificates.
DTLS add significat overhead, reduce the MTU to account for it
buffer plain text datagram until the DTLS handshake has completed
work arround for gnutls DTLS fragment bug