Makefile.inc1: make pkg-create(8) compression level overridable
pkg(8) after 8991ebd7afb0 ("Fix #1566: Add pkg-create(8) -l,--level
to set compression level") accepts compression level when creating
packages with a compression format (e.g. txz, tzst).
When compression is used (PKG_FORMAT is not "tar"), use compression
level from PKG_LEVEL for pkg-create(8) to make use of 8991ebd7afb0.
PKG_LEVEL default is set to pkg default to keep current behavior,
see pkg(8) 31000cb40b30 ("tzst: by default compression at the 19 level).
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1420