sys: Style fix for M_EXT | M_EXTPG

Add a space around the | operator in places testing for either M_EXT
or M_EXTPG.

Reviewed by: imp, glebius
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D43216

(cherry picked from commit f7d5900aa063c6e9d19e6372ba981fc76aa326a2)