AIX doesn't set the length in getsockopt.

[perl #120835] and [rt #91183] and [rt #85570]

Seen errors in blead smoke in AIX 6.1:

cpan/IO-Socket-IP/t/18fdopen .................................. Argument
"\0\0\0^A\0\0\0r\0\0\0\0\0\0\0\0?M-^U\0\0M-^E^[^???\0^N\0..." isn't
numeric in numeric eq (==) at ../../lib/IO/Socket/IP.pm line 748.

cpan/IO-Socket-IP/t/31nonblocking-connect-internet ............ Argument
"\0\0\0\0\0\0\0\0?\0\n^B1?\0\0\0^B\0^BM-\rf?^H?\0^N\0^B?|..." isn't
numeric in scalar assignment at ../../lib/IO/Socket/IP.pm line 707.
(cherry picked from commit ee2276e59a3c027cb89c721d866c9db4ba683a7b)
perldelta for the prev. commit

based on the entry in bb8c7e2708.