wolfssl: set nonshared flag global

wolfssl: set nonshared flag global

libwolfssl-benchmark should NOT be compiled as nonshared but
currently there is a bug where, on buildbot stage2, the package
is recompiled to build libwolfssl-benchmark and the dependency
change to the new libwolfssl version.
Each dependant package will now depend on the new wolfssl package
instead of the one previously on stage1 that has a different package
HASH.

Set the nonshared PKGFLAGS global while this gets investigated
and eventually fixed.

Fixes: 0a2edc2714dc ("wolfssl: enable CPU crypto instructions")
Signed-off-by: Christian 'Ansuel' Marangi <ansuelsmth@gmail.com>