"%m" can't be used to print strerror(errno), because print_on_level()
calls gettimeofday() which can overwrite errno.

For example:
13486 connect(4, {sa_family=AF_INET, sin_port=htons(8880), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 ENETUNREACH (Network is unreachable)
13486 gettimeofday({1423756664, 717423}, NULL) = 0
13486 open("/etc/localtime", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
13486 write(2, "15:57:44.717:     4: ERR: socket_udp.c:73: Can't connect (errno = 101 (Permission denied))\n", 91) = 91
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>