Fix the following -Werror warning from clang 3.5.0, while building
lib/libngatm:

sys/contrib/ngatm/netnatm/saal/saal_sscop.c:4030:32: error: 'break' is bound to current loop, GCC binds it to the enclosing loop [-Werror,-Wgcc-compat]

} while(sn < sscop->vr_h && !QFIND(&sscop->rbuf, sn));
                             ^

sys/contrib/ngatm/netnatm/saal/saal_sscop.c:173:4: note: expanded from macro 'QFIND'

break;                                          \
^

1 error generated.

The idea is to remove any ambiguity by replacing the macro with an
equivalent static inline function.

Reviewed by: emaste, rpaulo
See also: http://reviews.llvm.org/D2518
Differential Revision: https://reviews.freebsd.org/D1188