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.
Manually revert "Rationalise RX_MATCH_UTF8_set()"

Commit 0254aed965 says in its message, among other things:

    Now that the RXf_MATCH_UTF8 flag on a regex is just used to indicate
    whether the captures on a successful match are utf8, only set
    this flag at the end of a successful match, rather than at the start of
    the match.

But if we only set the utf8 flag at the end of the match, then $^N
accessed within the match will have the flag wrongly set.
(cherry picked from commit ab4e48c10a3551d7cfb88a2e29d82e0b499712e1)
[perl #123135] Tests for utf8 $^N within match

(cherry-picked from 9c6c921b)
perldelta for ab4e48c10a / #123135
(cherry picked from commit 53795ef8027c9585205bd1d0a78eca362ec8a453)