libbpf: Fix ELF symbol visibility update logic

Fix silly bug in updating ELF symbol's visibility.

Fixes: a4634922 ("libbpf: Add linker extern resolution support for functions and global variables")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210507054119.270888-6-andrii@kernel.org

tools/lib/bpf/linker.c

@@ -1788,7 +1788,7 @@ static void sym_update_visibility(Elf64_Sym *sym, int sym_vis)
 	/* libelf doesn't provide setters for ST_VISIBILITY,
 	 * but it is stored in the lower 2 bits of st_other
 	 */
-	sym->st_other &= 0x03;
+	sym->st_other &= ~0x03;
 	sym->st_other |= sym_vis;
 }