sfxge(4): removing unneeded assert

Remove ASSERT() from sfxge_link_mode_to_phy_cap() which causes an
unnecessary panic, even though the callers have proper error handling.

Submitted by:   Andy Moreton <amoreton at solarflare.com>
Sponsored by:   Solarflare Communications, Inc.
Differential Revision:  https://reviews.freebsd.org/D18167

sys/dev/sfxge/sfxge_port.c

@@ -896,7 +896,6 @@ sfxge_link_mode_to_phy_cap(efx_link_mode_t mode)
 	case EFX_LINK_40000FDX:
 		return (EFX_PHY_CAP_40000FDX);
 	default:
-		EFSYS_ASSERT(B_FALSE);
 		return (EFX_PHY_CAP_INVALID);
 	}
 }