Add custom union for handling both sockaddr_in/sockaddr_in6 structures

[ton31337]

In addition use two MACROs for allocating buffers to store IP addresses, thus saving some space.

(gdb) bt
#0  0x00007f6b1a22cfb3 in inet_ntop () from /lib64/libc.so.6
#1  0x0000000000456189 in MySQL_Thread::listener_handle_new_connection (this=0x7f6b1100d000, myds=0x7f6b1101a200, n=<optimized out>) at MySQL_Thread.cpp:2910
#2  0x000000000045d16e in MySQL_Thread::run (this=this@entry=0x7f6b1100d000) at MySQL_Thread.cpp:2452
#3  0x00000000004390d4 in mysql_worker_thread_func (arg=0x7f6b1863c990) at main.cpp:165
#4  0x00007f6b1b988dc5 in start_thread () from /lib64/libpthread.so.0
#5  0x00007f6b1a21eced in clone () from /lib64/libc.so.6

(gdb) x/16b &(*(struct sockaddr_in6 *)sess->client_myds->client_addr)->sin6_addr
0x7f6b021ffff8:	0x2a	0x02	0x47	0x80	0x0b	0xad	0xf0	0x0d
0x7f6b02200000:	Cannot access memory at address 0x7f6b02200000

[renecannao]

Thanks! Merged in master and v1.3.0