When given an IPv4 address, the string spliteAddr
receives looks like:
  1.2.3.4:123
Splitting on ":" is fine, because the IP address
contains only integers and "." chars.

When given an IPv6 address, the string spliteAddr
receives looks like:
  [2001:0db8:85a3:0000:0000:8a2e:0370:7334]:123

The existing implementation fails on such a string.
Colons are used within IPv6 addresses.

My patch splits on the last ":" character, which works
for both IPv4 and IPv6 addresses.