build_matrix.sh: Use the local libpcap before the system one

This means we'll catch any "make check" errors sooner.
("make check" is not run with system libpcap.)

Author: fxlb

build_matrix.sh

@@ -7,7 +7,7 @@
 # MATRIX_BUILD_LIBPCAP, MATRIX_REMOTE, MATRIX_CC, MATRIX_CMAKE, MATRIX_CRYPTO
 # and MATRIX_SMB.
 
-: "${MATRIX_BUILD_LIBPCAP:=no yes}"
+: "${MATRIX_BUILD_LIBPCAP:=yes no}"
 : "${MATRIX_REMOTE:=no}"
 : "${MATRIX_CC:=gcc clang}"
 : "${MATRIX_CMAKE:=no yes}"