libxencall: osdep_hypercall() should return long

libxencall: osdep_hypercall() should return long

Some hypercalls, memory-op in particular, can return values requiring
more than 31 bits to represent. Hence the underlying layers need to make
sure they won't truncate such values. (Note that for Solaris the
function also gets renamed, to match the other OSes.)

Due to them merely propagating ioctl()'s return value, this change is
benign on Linux and Solaris. IOW there's an actual effect here only for
the BSDs and MiniOS, but even then further adjustments are needed at the
xencall<N>() level.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <iwj@xenproject.org>