MFC r331641, r331644, r332158
Fix access to ifru_buffer on freebsd32.
Make all kernel accesses to ifru_buffer go via access functions
which take the process ABI into account and use an appropriate union
to access members in the correct place in struct ifreq.
Reviewed by: kib
Obtained from: CheriBSD
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D14846
Fix a whitespace bug missed in refactoring prior to r331641.
MFC with: r331641
Remove the thread argument from ifr_buffer_*() accessors.
They are always used in a context where curthread is the correct thread.
This makes them more similar to the ifr_data_get_ptr() accessor.