Fix static analysis issues.

• always check return values from socket related functions
• avoid doublefree in udp_cleanup() and icmp_cleanup()
• use secure string manipulation in icmp_send_error()
• always initialize addr local structure in udp_listen()
• check if lseek() fails in tftp_read_data()

Signed-off-by: Jindrich Novy jnovy@redhat.com