boot_serial; re-enable mynewt boot_serial unittests.

Signed-off-by: Marko Kiiskila <marko@runtime.io>
diff --git a/boot/boot_serial/src/boot_serial.c b/boot/boot_serial/src/boot_serial.c
index 9b63043..6257613 100644
--- a/boot/boot_serial/src/boot_serial.c
+++ b/boot/boot_serial/src/boot_serial.c
@@ -71,7 +71,7 @@
 #endif
 static char in_buf[BOOT_SERIAL_INPUT_MAX + 1];
 static char dec_buf[BOOT_SERIAL_INPUT_MAX + 1];
-static const struct boot_uart_funcs *boot_uf;
+const struct boot_uart_funcs *boot_uf;
 static uint32_t curr_off;
 static uint32_t img_size;
 static struct nmgr_hdr *bs_hdr;