MFC r261075: Update EINVAL description.
MFC r261084:
  malloc() with M_WAITOK doesn't return NULL.

MFC r261085:
  Fix typo in r261084.
  Add to the gctl_error() an ability to specify error description even
  if numeric error code is already specified. Also by default set
  error code to EINVAL.

  PR:		185852

MFC r261086:
  In gctl_copyin() remove unused error variable.
  geom_alloc_copyin() can't return ENOMEM, so describe its fail as bad
  control request. Add check for NULL pointer in gctl_dump(), since it
  can be NULL when geom_alloc_copyin() failed.

MFC r261089:
  Remove another unneeded NULL check from geom_alloc_copyin().
  Do copyout in case of gctl version mismatch and fix sbuf leak in
  g_ctl_ioctl_ctl().

MFC r261091:
  Always free sbuf in gctl_free().